#include <fstream>
#include <iostream>
#include <string.h>

using namespace std;

ifstream in("ciur.in");
ofstream out("ciur.out");

int main()
{
        int N;
        in >> N;
        int vec[N];
        int val = 0;
        for(int i = 2; i <= N; i++)
                vec[i] = 0;
        for(int i = 2; i <= N; i++)
        {
                if(vec[i] == 0) {
                        val++;
                        for(int j = i*2; j <= N; j += i)
                                vec[j] = 1;
                }
        }
        out << val;
        return 0;
}